1. Field of the Invention
The present invention relates generally to an air conditioning system for a vehicle. More specifically, the invention relates to an automotive air conditioning system for controlling blower speed for adjusting conditioning air discharge rate depending upon a temperature deviation between a cabin temperature and a set temperature, and ambient temperature and insolation.
2. Description of the Related Art
A typical construction of a blower control system for an automotive air conditioning system has been disclosed in Japanese Examined Patent Publication (Kokoku) No. 62-41128. The disclosed system is designed so as to increase blower speed when insolation is increased at an operational range, in which a deviation between a cabin temperature and a set temperature is small, for enhancement of feeling of the passengers in a vehicular cabin.
In such prior art, when the blower speed is limited so as not to become excessive during cooling at an extremely hot cabin condition, such as that upon entering after excessive exposure to insolation, or during cold conditions in the winter, an air conditioning discharge rate at a steady state may be insufficient to maintain a uniform temperature distribution within the cabin and cause substantial deviation between the cabin temperature and the set temperature by external disturbance of the thermal load
In view of such a defect in the prior art, there is a prior invention filed under Japanese Patent Application No. 1-166529, that has been assigned to the common assignee of the present invention. The disclosure of the above-identified Japanese Patent Application is herein incorporated by reference for the sake of disclosure. The shown system is intended to suppress a noise level by lowering the conditioned air discharge rate during the transition state and maintain uniformity of temperature distribution within the cabin by increasing the conditioned air discharge rate during steady state operation. The shown air conditioning system includes a control system. The control system derives a demanded discharge air temperature on the basis of the set temperature, a cabin temperature, an ambient temperature and the insolation for a transition period, such as during the cooling down state or warming up state. The control system further derives a first blower voltage corresponding to the demanded discharge air temperature for the transition state. The control system also derives a demanded discharge air temperature for the steady state on the basis of the input information, i.e., set temperature, the cabin temperature, the ambient temperature and the insolation, and a second blower voltage corresponding to the demanded discharge air temperature for the steady state. The first and second blower voltages are compared so that a greater value of the blower voltages is selected and supplied to a blower drive control system as a blower control voltage.
Although the prior proposed systems as set forth above provide a certain level of gain in enhancement of the automotive air conditioning system, they are still unsatisfactory and can encounter some problems. For example, considering the operation of the above-mentioned air conditioning system in relatively cold weather, such as in the winter, when insolation is detected, the control system adjusts the demanded discharge air temperature Tao for a lower temperature due to the presence of insolation. Since the blower voltage is derived relative to the discharge air temperature Tao, the blower voltage can be accordingly lowered. For instance, assuming that the discharge air temperature Tao-blower voltage Vb characteristics is set as shown in FIG. 9 and further assuming that the demanded discharge air temperature is varied from the point A, in which no insolation is present, to the point B, in which the insolation is present, the blower voltage becomes the value corresponding to the demanded discharge air temperature Tao at the point B. Therefore, the blower speed is lowered to reduce the discharge rate of the conditioning air. At the same time, discharge air temperature control is performed in the per se known manner to adjust the air mix door open angle toward the cooler side for lowering the discharge air temperature according to the reduction of the demanded discharge air temperature Tac, as shown in FIG. 11. It is further assumed that the discharge mode of the conditioning air is maintained in FOOT (HEATER) mode, the reduced flow rate of the conditioning air with the lowered temperature should be discharged.
However, since the conventional control system is designed so as to increase the discharge rate of the conditioning air in response to insolation, insolation dependent correction for the blower speed is performed in response to insolation. By this, the discharge rate of the lowered temperature conditioning air is increased to be discharged through FOOT vents. This may create a cool feeling directly subjecting the occupants to the increased flow rate of the lowered temperature conditioning air.
Also, in the conventional air conditioning system, in a relatively warm environment, such as midday in the winter or spring or fall, insolation may provide a hot feeling for the passengers directly subjected to the sun beam. Despite the hot feeling due to insolation, the control system can maintain FOOT mode operation in certain environmental conditions with a reduced conditioning air discharge rate by the presence of insolation. In such occasions, the upper body of the passenger subject to an incoming sum beam, may not be satisfactorily cooled due to insufficient amount of conditioning air discharged into the cabin, and due to a discharge mode selected for directing conditioning air toward the lower body of the passenger. This clearly degrades the comfort of the passengers.
Such shortcoming is caused by the presence of the operational range of the air conditioning system in which a discharge mode is maintained in the FOOT mode while the demanded discharge air temperature Tao is lowered due to presence of insolation. Also, an algorithm for increasing the conditioning air discharge rate in a straightforward manner in response to the presence of insolation cannot optimize the operation of the air conditioning system over all environmental conditions, and serves to cause an uncomfortable feeling in certain environmental conditions such as that discussed above.